1. Field of the Invention
The present invention relates to an image processing apparatus and an interpolation frame generating method that generate an interpolation frame between frames of an input image.
2. Description of the Related Art
Recently, in an image processing apparatus such as television, it is becoming common to insert an interpolation frame between frames of an input image and to output the image. In this way, the image is output at a frame rate higher than the input frame rate, which provides a moving image which is smooth and has a small blurring. It is common that the interpolation frame to be inserted is generated based on the previous and subsequent frames and a motion vector between the frames which is estimated from the difference between continuous frames of the input image (see Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-245135 and Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2010-278760).
Incidentally, in a case of generating each pixel of an interpolation frame, it is assumed that a target pixel is present in a frame of interpolation source. Thus, when a target pixel is not present in a frame of interpolation source, precision of interpolation will be lowered. This generates a frame which provides a feeling of strangeness to a viewer of the image. Such feeling of strangeness remarkably occurs at the screen edge (edge portion of the screen).
That is, when an object is moving at the screen edge, there may be a case where the original pixel is not present on the screen in one of the previous and subsequent frames, which are the interpolation source of the interpolation frame, by the object fading in or out of the screen and going outside of the screen. If the outside-screen pixel is used for the interpolation source as is, an interpolation error may occur since an ordinary image data is generally not present outside the screen.
Thus, according to the Patent Literature 1, in order to avoid using the outside-screen pixels as the interpolation source, only one of the previous and subsequent frames is used as the interpolation source at the screen edge. That is, as shown in FIG. 1, a pixel of the subsequent frame if where a motion vector denoted by a broken line points the outside-screen pixel is not used, and only a pixel of the previous frame 0f where a motion vector points the inside-screen pixel is used. In this method, when the detection precision of the motion vector is not high, a sharp change occurs at the boundary between the interpolation pixel generated by using two frames and the interpolation pixel generated by using only one frame, which enhances a risk of causing the feeling of strangeness felt by the viewer of the image.